Polycarbonate resins are well-known thermoplastic resins which have long been used in a variety of applications requiring resistance to impact. At low temperatures, generally lower than 20.degree. C., polycarbonate becomes brittle and its utility is thus limited by this shortcoming. It is known that the low temperature impact strength of polycarbonate may be improved upon by the introduction (by copolymerization) of silicone blocks into the carbonate structure. U.S. Pat. Nos. 3,189,662; 3,419,634; 4,123,588; 4,569,970; 4,920,183 and 5,068,302 are noted to disclose relevant copolymers.
Relevant copolymers have been prepared in accordance with a melt blending process disclosed in U.S. Pat. No. 4,994,532. The process entails melt blending an aromatic polycarbonate resin and a polydiorganosiloxane having at least one functional carboxylic acid group. Also relevant in the present context is U.S. Pat. No. 4,657,989 which disclosed a preparation method where siloxane compound is reacted with polycarbonate, wherein at least one of the reactants is anionic and the other being reactive with nucleophiles.
Most relevant is the disclosure in U.S. Pat. No. 5,414,054 which disclosed reactive blending of polycarbonate with a lactone siloxane copolymer in the presence of a catalyst. The resulting compositions exhibit improved low-temperature impact strength.